Blown diffusers is way more complicated subject than previous seasons.

Neither does any upgrades for the past two years.

Its not a simple rule as who has blown diffusers will dominate, to make it work with the entire package is tough. Same goes to the past two years. But McLaren and Ferrari had shown us they are capable to catch up during the course of the season. I won't be surprised later this year they will somewhat close to RBR's pace.